1. Field of the Invention
The present invention relates to a portable engine unit, and more particularly to a portable engine unit applicable for a weed cutter, snow blower, etc., and has a housing which is separated along a plane including the axis of rotation of an output shaft of the engine.
2. Description of the Prior Art
In a prior art portable engine unit, a housing which encloses an engine is divided along a plane orthogonal to the axis of rotation of an output shaft of the engine and provided with two cover casings which are fitted to the opposite sides of the housing. Further, in many prior art portable engine units, separate casings shall be provided for enclosing a cylinder, muffler, etc., of the engine. As a result, the number of parts are increased to complicate the processing and assembling works of engine.
A prior art portable weed cutter, etc., which comprises a portable engine unit and a cutter is provided with a handle which is usually fixed to a connection pipe for connecting the engine with the cutter. This location of the handle tends to cause a problem that the whole length of the weed cutter becomes longer.
Measures to cope with noise and vibration are not sufficiently realized in a prior art portable engine unit. For instance, in some prior art portable engines, suction holes are provided on a side face of a housing of engine to cause a large suction noise. In the vicinity of the suction holes, an air filter is usually disposed in a separate air filter case which occupies a relatively large space in the housing to limit the size of air filter that again leads to a large suction noise. To reduce exhaust noise, a muffler is provided. A prior art muffler provided for a portable engine is usually welded to the engine that complicates the manufacturing process and the maintenance work of muffler. Further, the high temperature of exhaust gas is not sufficiently cooled by the prior art muffler so that an operator may get burnt and the engine may be damaged due to the high temperature of exhaust gas. A spark arrestor for catching fire in exhaust gas is attached between the base of prior art muffler and an exhaust port of the engine. This location of spark arrestor causes a maintenance work such as cleaning of the spark arrestor to be difficult.
Concerning vibration, a prior art portable engine is provided with a plurality of vibration isolators between the engine and a housing of the engine. The engine comprises a crankcase enclosing a cantilever crank arm, a recoil starter, a magnet wheel, and a centrifugal clutch comprising a clutch drum and a clutch shoe member. These components are arranged axially in series to constitute the engine. The vibration isolators are positioned around the engine gravity center which is usually located in front of the crankcase. In this arrangement, the gravity center of reciprocating parts such as a piston and a piston rod, which are main factors of vibration, are positioned out of an area surrounded by the vibration isolators. As a result, vibration is not effectively prevented.
As another measure to cope with vibration, the prior art portable engine is equipped with a vibration isolator joint between the centrifugal clutch and a torque transmission shaft which transmits torque generated by the engine through the clutch to a work tool such as a weed cutter. In order to house the vibration isolator joint and the clutch drum, a special casing is required that increases the manufacturing process and cost as well as the weight of engine.
For cooling the engine, the prior art portable engine is provided with a fan which is fixed to a crank shaft of the engine, and a spiral passage for guiding airflow generated by the fan to the periphery of engine. Due to the spiral configuration of the airflow passage, the overall size and weight of the engine tend to become large.